1. Field of the Invention
The present invention relates to biasing circuitry for generating stable biasing signals and in particular, to biasing circuitry for generating and maintaining substantially constant output bias currents notwithstanding variations in circuit fabrication processes, power supply voltage, and operating temperature.
2. Description of the Related Art
Amplifier operating efficiency is important in virtually all circuit applications. However, this is particularly true for power amplifiers in radio frequency (RF) circuit applications, especially for mobile devices. In many such applications, particularly for mobile devices, such circuitry will often be required to operate over variations in temperature and power supply voltages. Further, variations in the fabrication or other manufacturing processes in producing such circuitry can also induce undesirable variations in operating characteristics.
Biasing circuitry in accordance with the presently claimed invention generates and maintains a substantially constant output bias current. Ratios of selected bias currents and selected transistor sizes ensure that a nominal, or average, load current is maintained notwithstanding variations in circuit fabrication processes, power supply voltage and operating temperature.
In accordance with one embodiment of the presently claimed invention, biasing circuitry for generating and maintaining a substantially constant output bias current notwithstanding variations in circuit fabrication processes, power supply voltage and operating temperature includes first current replication circuitry, second current replication circuitry and a reference transistor. The fast current replication circuitry receives a reference current having a magnitude Iref and in response thereto generates a bias signal and a first replica current having a magnitude N*Iref. The second current replication circuitry, coupled to the first current replication circuitry, receives the bias signal and in response thereto generates a branch current having a magnitude Ib and a second replica current having a magnitude M*Ib. The reference transistor, coupled to the first and second current replication circuitry, receives the branch current as an input current and conducts the first replica current as an output current.
In accordance with another embodiment of the presently claimed invention, biasing circuitry for generating and maintaining a substantially constant output bias current notwithstanding variations in circuit fabrication processes, power supply voltage and operating temperature includes first current replicator means, second current replicator means and reference transistor means. The first current replicator means is for receiving a reference current having a magnitude Iref and in response thereto generating a bias signal and a first replica current having a magnitude N*Iref. The second current replicator means is for receiving the bias signal and in response thereto generating a branch current having a magnitude Ib and a second replica current having a magnitude M*Ib. The reference transistor means is for receiving the branch current as an input current and conducting the first replica current as an output current.